The invention relates to an electric heating element, particularly to an element suitable for hair dryers.
Heating elements for hair dryers should be as short as possible in order to reduce the weight of the appliance and to make it easy to handle; on the other hand it should present an adequate heat transfer surface while offering a minimum of flow resistance, with a view to permit the provision of a small fan and fan motor in the dryer. In the past I have found that the most suitable heating element answering the above requirements is in the shape of a ribbon-shaped resistor helically wound on a spider-shaped core, in such a manner that the ribbon surfaces of all windings are parallel to the air flow. This design ensures a minimum of flow resistance, since the front surface offered to the air flow by the thin resistor is very small compared with the total heat exchange area. A high heat exchange coefficient is attained by the air spaces between adjoining coil windings, because they interrupt the boundary layer apt to form along a plain continuous surfaces, and thus create air turbulence.
Although this type of heater coil gives very good results, I have now discovered that I can still improve the heat transfer by staggering successive windings and thus obtain a shorter total length of the element by providing less windings which, however, dissipate the same heat energy through a smaller exchange surface by virtue of increased turbulence.